Aluminum-based bearing alloy and production method of the same

ABSTRACT

An Al-based bearing alloy containing 1 to 15 mass % of Si is provided. The Al-based bearing alloy includes Si particles, and a total length of circumference of the Si particles observed in an observation field of 37820 μm 2  on a slide side surface is 4000 to 6000 μm.

TECHNICAL FIELD

The present invention relates to an Al (aluminum) based bearing alloycontaining Si (silicon) and a production method thereof.

BACKGROUND OF THE INVENTION

A slide bearing including an Al-based bearing alloy on a substrate hasrelatively satisfactory initial conformability, and high fatigueresistance under high specific load, and thus it is used in an internalcombustion engine of an automobile.

An Al-based bearing alloy having higher fatigue resistance is disclosedin, for example, JP-A-3-6345. The Al-based bearing alloy in JP-A-3-6345contains 1 to 15 mass % of Si and 0.005 to 0.5 mass % of Sr. JP-A-3-6345discloses that the Al-based bearing alloy contains Sr in order to have afine size of a Si particle, and that the Al-based bearing alloy can bearhigh loads and is prevented from being brittle due to the fine Siparticle, thereby improving fatigue resistance of the Al-based bearingalloy.

SUMMARY OF THE INVENTION

In recent years, an Al-based bearing alloy having high seizureresistance besides fatigue resistance is desired. Specifically, in thefield of a recent internal combustion engine, a connecting rod or thelike has reduced thickness to reduce a weight of the internal combustionengine in order to improve fuel consumption. The reduction in thicknessof the connecting rod reduces rigidity of the connecting rod, and theconnecting rod is easily deformed. Thus, a slide bearing provided in theconnecting rod is also easily deformed. Thereby, a sliding counterpartmember easily comes into local contact with a slide side surface of theAl-based bearing alloy. If the counterpart member continues to slidewhile being in direct contact with the Al-based bearing alloy, seizuremay occur.

The present invention is achieved in view of the above-describedcircumstances, and has an object to provide an Al-based bearing alloyhaving high seizure resistance and a production method thereof.

The inventors have noted a size of a Si particle in an Al-based bearingalloy containing 1 to 15 mass % of Si and diligently repeatedexperiments. As a result, the inventors have found that even if acontent of Si particles is the same in the Al-based bearing alloycontaining 1 to 15% by mass of Si, satisfactory seizure resistance ofthe Al-based bearing alloy can be obtained when a total length ofcircumferences of Si particles observed in a predetermined range of anobservation field on a slide side surface is within a predeterminedrange.

The inventors have achieved the invention described below based on theabove finding.

The present invention provides an Al-based bearing alloy containing 1 to15 mass % of Si, wherein a total length of circumference of Si particlesobserved in an observation field of 37820 μm² on a slide side surface is4000 to 6000 μm.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of an Al-based bearing alloy according to anembodiment of the present invention;

FIG. 2 is a conceptual view illustrating a region partitioning method;

FIG. 3 is a side view showing a schematic configuration of a castingdevice; and

FIG. 4 is a side view schematically showing a rolling step.

DETAILED DESCRIPTION OF THE INVENTION

As an Al-based bearing alloy of the present invention, an embodiment ofan Al-based bearing alloy layer on a substrate of a slide bearing willbe explained below. The Al-based bearing alloy may be used as a slidemember (slide bearing) rather than formed on a back metal layer.

First, an embodiment of the Al-based bearing alloy is shown in FIG. 1. Aslide bearing 1 in FIG. 1 includes a substrate 2 and an Al-based bearingalloy (Al-based bearing alloy layer) 3 on the substrate 2. In FIG. 1, asurface on a slide side (sliding counterpart member side) of theAl-based bearing alloy 3 is denoted by “surface 3 a”.

The substrate 2 is a member on which the Al-based bearing alloy 3 isformed, and it is, for example, a back metal layer made of steel, iron,or the like.

As shown in FIG. 2, the Al-based bearing alloy 3 contains 1 to 15 mass %of Si (Si particles 5) in a matrix 4 of Al or an Al alloy. Withincreasing an amount of Si in the Al-based bearing alloy 3, the Al-basedbearing alloy 3 becomes harder and fatigue resistance of the slidebearing 1 is increased. When Si contained in the Al-based bearing alloy3 is 1% by mass or more, there is an influence of Si on hardness, and aneffect of increased fatigue resistance of the slide bearing 1 can beobtained. When Si contained in the Al-based bearing alloy 3 is 15 mass %or less, the Al-based bearing alloy 3 can be prevented from beingbrittle.

The Al-based bearing alloy 3 contains inevitable impurities.

In the embodiment, a total circumferential lengths of Si (Si particles5) observed in an observation field of 37820 μm² on a surface 3 a of theAl-based bearing alloy 3 is 4000 to 6000 μm. The surface 3 a of theAl-based bearing alloy 3 is observed by an optical microscope. Theobservation field can be changed by adjusting an observation range ofthe optical microscope, and the observation field is determined to be37820 μm² in the embodiment.

A circumferential length of each Si particle 5 observed by the opticalmicroscope is measured using image analysis software, for example,Image-Pro Plus (Version 4.5) (trade name) (produced by Planetron, Inc.).

In the embodiment, the total circumferential lengths of the Si particles5 observed in the observation field of 37820 μm² on the surface 3 a ofthe Al-based bearing alloy 3 is a predetermined length or more, that is4000 μm or more in the embodiment, to increase an interface area betweenthe matrix 4 and the Si particles 5. This increases interface energy atinterfaces between the matrix 4 and the Si particles 5, and the increasein the interface energy increases surface energy of the surface 3 a ofthe Al-based bearing alloy 3, thereby increasing wettability of alubricant on the surface 3 a. Such increased wettability of the surface3 a prevents oil film break. Thus, according to the embodiment,wettability of the surface 3 a can be increased to prevent directcontact between the Al-based bearing alloy 3 and a counterpart member.This provides satisfactory seizure resistance of the Al-based bearingalloy 3.

In the embodiment, the total circumferential lengths of the Si particles5 observed in the observation field of 37820 μm² on the surface 3 a ofthe Al-based bearing alloy 3 is 6000 μm or less. When the totalcircumferential lengths of the Si particles 5 is 6000 μm or less, thematrix 4 does not include so many Si particles 5 that make the matrix 4too hard. This provides satisfactory conformability of the Al-basedbearing alloy 3 in the embodiment.

For the Al-based bearing alloy of the present invention, preferably, theobservation field of 37820 μm² on the slide side surface is divided intoregions, each region including one Si particle by a region partitioningmethod. Preferably, an average aspect ratio of the regions is 1 to 2.

The region partitioning method is shown in FIG. 2. A line (in theembodiment, the Si particles 5 in the observation field are convertedinto volonoi polygons and a boundary of the volonoi polygons correspondto the “line”) is drawn between adjacent Si particles 5 in theobservation field on the surface 3 a of the Al-based bearing alloy 3,and the observation field is divided into regions. The number of theregions is same as the number of the Si particles 5. In this embodiment,the observation field of 37820 μm² on the surface 3 a of the Al-basedbearing alloy 3 is divided into regions for the respective Si particles5 to be observed by the region partitioning method.

With the same content of Si (Si particle 5), the size of the Si particle5 and the number of the Si particles 5 have a correlation. When the Siparticle 5 is large, the number of the Si particles 5 is small, therebyincreasing an area of each region obtained by the region partitioningmethod. On the other hand, when the Si particle 5 is small, the numberof the Si particles is large, thereby reducing the area of each region.

The “aspect ratio of the region” refers to a ratio of length of a majoraxis to length of a minor axis of the region, that is, a value obtainedby dividing the length of the major axis by the length of the minoraxis. The major axis herein refers to a maximum length in a regionobtained by the region partitioning method. The minor axis refers to alength in a direction passing through a center of the major axis andperpendicular to the major axis in the region.

The “average aspect ratio” in the embodiment is an average value ofaspect ratios of the respective regions in the observation fieldobtained by the region partitioning method. The observation field in theembodiment is 37820 μm².

In the embodiment, the average aspect ratio of the regions is 1 to 2.When the average aspect ratio of the regions is closer to 1, each regionhas a more circular or equilateral polygonal shape. The Si particles 5are more uniformly dispersed in the matrix 4, and surface energy becomesmore uniform on the entire surface 3 a of the Al-based bearing alloy 3.Thus, uniform wettability can be obtained on the entire surface 3 a ofthe Al-based bearing alloy 3 to prevent local oil film break. This alsoprovides satisfactory seizure resistance of the Al-based bearing alloy3.

The slide bearing 1 is produced by a casting step, a rolling step, aroll bonding step, a heat treatment (annealing) step, and a machiningstep.

A production method of an Al-based bearing alloy of the presentinvention preferably includes the steps of: melting Al or an Al alloyand Si to produce a molten alloy; cooling the molten alloy at a rate of80° C./sec to 130° C./sec to form an Al-based cast plate; and rollingthe Al-based cast plate at a reduction of 50% to 95% to produce theAl-based bearing alloy.

In the casting step, the molten metal is obtained by melting Si with Alor an Al alloy and is cast at a cooling rate of 80° C./sec to 130°C./sec to produce the Al-based cast plate. The Cooling rate of themolten metal causes molten. Si to be crystallized in a matrix 4. The Si(Si particles 5) is finer than conventional Si (Si particles).

In a rolling step, the Al-based cast plate is rolled by a roller or thelike, to produce the Al-based bearing alloy 3. Rolling is performeduntil a reduction in the rolling step reaches 50% to 95%. While rollingpass may be conducted at any number of times, preferably it is once tofive times.

The term “reduction” indicates a degree of rolling as compared with astate before rolled (before the rolling step). The reduction Z (%) isexpressed by a formula:

Z={(X−Y)/X}×100(%)

Where X (mm) is a plate thickness before rolled (before the rollingstep), and Y (mm) is a plate thickness after rolled (after rollingstep).

According to the embodiment, the Al-based cast plate obtained by thecasting step is rolled at a reduction of 50% or more, and thus theAl-based bearing alloy 3 can be obtained in which the totalcircumferential lengths of the Si particles 5 observed in an observationfield of 37820 μm² on the surface 3 a is 4000 μm or more.

According to the embodiment, the Al-based cast plate obtained by thecasting step is rolled at a reduction of 95% or less, and thus theAl-based bearing alloy 3 can be obtained in which the totalcircumferential lengths of the Si particles 5 observed in an observationfield of 37820 μm² on the surface 3 a is 6000 μm or less.

In the roll bonding step, the Al-based bearing alloy 3 obtained in therolling step is roll-bonded to a substrate (back metal layer) 2, toproduce a bearing forming plate material.

Then, the bearing forming plate material obtained by the roll bondingstep is annealed by a heat treatment (annealing) step, and machined by amachining step to produce a semicircular or circular slide bearing 1.

Although the slide bearing 1 having a two-layer structure including thesubstrate 2 and the Al-based bearing alloy 3 is described, it may have athree-layer structure including an adhesive layer, for example anintermediate layer of pure Al or the like between the Al-based bearingalloy 3 and the substrate 2. Also, an overlay layer of Bi, Sn, a Bialloy, a Sn alloy, or the like may be formed on the Al-based bearingalloy 3. When the overlay layer is applied on the Al-based bearing alloy3, seizure resistance of the Al-based bearing alloy 3 is exhibited afterthe overlay layer wears.

The Al-based bearing alloy 3 may be subjected to solution treatment toincrease strength of the Al-based bearing alloy 3.

Examples

In order to confirm advantages of the embodiment, samples (Examples 1 to5 and Comparative examples 11 to 13) of slide bearings includingAl-based bearing alloys containing compositions shown in Table 1 wereproduced, and seizure tests of the samples were conducted.

TABLE 1 Total Maximum circumferential specific load Composition ofAl-based length of Si Average without bearing alloy (mass %) Coolingrate Reduction particles aspect ratio of seizure Sample Al Si (° C./sec)(%) (μm) regions (MPa) Example 1 Bal. 6 80 90 4185 1.3 90 2 Bal. 8 10095 5006 1.2 95 3 Bal. 6 100 90 5848 1.8 90 4 Bal. 3 100 80 4233 1.9 85 5Bal. 10 130 50 5000 2.2 80 Comparative example 1 Bal. 6 100 40 3200 1.370 2 Bal. 10 70 60 7941 2.1 65 3 Bal. 3 70 40 2409 2.2 65

Production methods of Examples 1 to 5 are as described below. First, Aland Si are melted at ratios shown in Table 1, and then cast with acasting device 11 shown in FIG. 3.

The casting device 11 includes a melting furnace 12 that storesmaterials for casting. Materials to be melted having the compositionsshown in Table 1 are charged in the melting furnace 12. The compositionsin Table 1 contain inevitable impurities.

The casting device includes a bath 13 for storing molten metal pouredfrom the melting furnace 12.

The bath 13 is provided with a molten metal supply nozzle 14 thatdischarges the molten metal stored in the bath 13. On a tip side of themolten metal supply nozzle 14, a pair of rollers 15, 15 with a minutegap therebetween are placed. The pair of rollers 15, 15 are placed sothat axes thereof extend horizontally in a direction perpendicular to aflow of the molten metal. Thus, the molten metal in the melting furnace12 passes through the bath 13 and the molten metal supply nozzle 14 andis supplied between the pair of rollers 15, 15.

The pair of rollers 15, 15 are cooled by cooling means such as a coolingpipe 16. A plurality of cooling pipes 16 extends axially in the pair ofrollers 15, 15. A coolant such as water is supplied into the coolingpipes 16 to cool the pair of rollers 15, 15. An amount of the watersupplied into the cooling pipes 16 and a flow rate thereof are adjusteddepending on a degree of opening and closing of an unshown valvecontrolled by an unshown control device. In production of Examples 1 to5, the degree of opening and closing of the valve is adjusted so as tocool the molten metal supplied between the pair of rollers 15, 15 fromthe molten metal supply nozzle 14 at a cooling rate of 80° C./sec to130° C./sec (cooling rate shown in Table 1). Cooling at 80° C./sec to130° C./sec is performed until the molten metal reaches 550° C.

The molten metal is cooled and solidified by the pair of rollers 15, 15to produce an Al-based cast plate 17. The obtained Al-based cast plate17 is cut to a predetermined length by a cutter 18 and wound by a toiler19. Then, the Al-based cast plate 17 is rolled by a pair of rollers 20,20 shown in FIG. 4 in the rolling step until a reduction reaches a valueshown in Table 1.

Then, the Al-based cast plate 17 having reached a predeterminedreduction is roll-bonded to a steel plate forming the substrate (backmetal layer). Thus, a bearing forming plate material is produced. Thebearing forming plate material is heated for several hours to beannealed and then machined to produce a slide bearing. Thus, the slidebearing was produced for Examples 1 to 5.

On the other hand, a production method of Comparative examples 11 to 13is different from the production method of Examples 1 to 5 in thefollowing points.

Comparative example 11 was obtained by the same production method asExamples 1 to 5 except that the reduction in the rolling step was 40%.

Comparative example 12 was obtained by the same production method asExamples 1 to 5 except that the cooling rate in the casting step was 70°C./sec.

Comparative example 13 was obtained by the same production method asExamples 1 to 5 except that the cooling rate in the casting step is 70°C./sec, and the reduction in the rolling step is 40%.

For thus obtained Examples samples 1 to 5 and Comparative examples 11 to13, a surface of each sample was observed, and a seizure test wasconducted under a test condition shown in Table 2. The results thereofare shown in Table 1.

For “total circumferential lengths of Si particles” and “Average aspectratios of regions” of Examples 1 to 5 and Comparative examples 11 to 13in Table 1 were measured by photographing a microstructure with anoptical microscope and analyzing an image in an observation field of37820 μm² using image analysis software, for example, Image-Pro Plus(Version 4.5) (trade name) (produced by Planetron, Inc.).

TABLE 2 Seizure test conditions RPM 8000 rpm Test load Increase by 5 MPaper 5 min Lubrication temperature  100° C. Lubrication amount  60 ml/minLubricant VG22 Material of shaft S55C Evaluation method Seizure isidentified when a bearing back surface temperature exceeds 200° C., or ashaft drive belt slips due to a torque change.

Next, the results of the seizure test are analyzed.

From comparison between Examples 1 to 5 and Comparative examples 11 and13, it is understood that Examples 1 to 5 have high seizure resistancebecause the total circumferential lengths of the Si particles is 4000 μmor more.

From comparison between Examples 1 to 5 and Comparative example 12, itis understood that Examples 1 to 5 have high seizure resistance becausethe total circumferential lengths of the Si particles is 6000 μm orless.

From comparison between Examples 1 to 4 and Example 5, it is understoodthat Examples 1 to 4 have extremely high seizure resistance because anaverage aspect ratios of regions obtained by the region partitioningmethod is 2 or less.

The present invention may be changed and carried out without departingfrom the spirit of the invention.

1. An Al-based bearing alloy containing 1 to 15 mass % of Si, theAl-based bearing alloy including Si particles, wherein a total length ofcircumference of the Si particles observed in an observation field of37820 μm² on a slide side surface is 4000 to 6000 μm.
 2. The Al-basedbearing alloy according to claim 1, wherein when the observation fieldof 37820 μm² on the slide side surface is divided into regions by aregion partitioning method, each region including one Si particle, anaverage aspect ratio of the regions is 1 to
 2. 3. A production method ofan Al-based bearing alloy comprising steps of: melting Al or an Al alloyand Si to produce a molten alloy; cooling the molten alloy at a rate of80° C./sec to 130° C./sec to form an Al-based cast plate; and rollingthe Al-based cast plate at a reduction of 50% to 95% to produce theAl-based bearing alloy.